1. Field of the Invention
The present invention relates in general to devices for removing obstructions from vessels or small openings in the body, and more particularly to a rotatable ablator tip which is guided to the obstruction in a reduced diameter configuration, expanded and rotated to remove the obstruction, and contracted to remove the device from the body.
2. Background Art
There has been great interest of late among those in the medical community in non-surgical means to remove obstructions from occluded vessels, particularly coronary arteries. Traditionally, patients have had to undergo relatively complex, invasive, and risky coronary bypass surgery in order to obviate or reduce the obvious health hazards presented by occluded coronary arteries. Coronary bypass surgery typically involves utilizing vascular tissue from another part of the patient's body, such as his leg, and constructing a shunt around the obstructed vessel. The obstruction can be formed of a relatively hard material, such as a plaque deposit, or a softer material such as a fibrinogen polymerized to form a thrombus.
An alternative to the traditional coronary bypass surgery which has become popular in recent years is a technique known as balloon angioplasty. In this technique, a deflated balloon is introduced by means of a catheter to the obstructed area. The balloon is then inflated to open the lumen of the vessel. The inflated balloon tends to crush or compact the obstructing material against the vessel walls as well as crack the obstructing material and dilate the vessel so as to increase the lumen or passageway therethrough, but does not remove the obstructing material from the vessel. Since the cracked and fractured obstructing material is not removed, there is a significant possibility that the vessel will become reoccluded at the treated area within a relatively short period of time, thus requiring additional treatment(s). The balloon angioplasty procedure has several additional drawbacks which tend to further reduce its desirability and/or effectiveness. In the case of a severely occluded vessel, it may be difficult to position the deflated balloon so that it spans the occlusion without causing undue trauma to the surrounding vasculature. This is because the leading portion of the balloon must first be forced through the occlusion into position for treatment. The balloon angioplasty procedure is not satisfactory for treating calcified and hard occlusions, since it may not be able to crack and dilate the obstructing material. The balloon angioplasty procedure also is not satisfactory for treating eccentric occlusions, i.e., occlusions which occur primarily on one side of the vessel, because the balloon tends to simply stretch the healthy vascular tissue and not to compress the occluding material. After the balloon is deflated, the healthy vascular tissue returns to its normal shape and the occlusion remains essentially untouched. Moreover, the balloon angioplasty technique is less suitable for treating lengthy occlusions or those occurring at curves and bends in the vessels, due to the difficulty of appropriately placing and properly inflating the balloons without the high risk of dissections. In addition, during the balloon angioplasty technique, there is a period of time during which the vessel is essentially totally obstructed by the balloon. This could lead to further damage to tissues already damaged, or even to damage to previously healthy tissues. Moreover, when the balloon inflates, it may cause uncontrolled deep injury to the vessel, including the formation of intraluminal flaps, which may in turn result in abrupt closure or predispose to a high rate of restenosis.
Atherectomy is another technique developed of late for opening the lumen of an occluded vessel, and, like the balloon angioplasty technique, provides an alternative to the traditional coronary bypass surgery. Atherectomy involves physically breaking up the material which blocks or partially blocks the vessel. Several types of atherectomy devices have been developed. U.S. Pat. Nos. 4,990,134 and 4,445,509 to Auth disclose a rotatable burr with a fluted or abrasive surface that is introduced into the obstructed vessel. At the obstruction the burr is rotated at a high rate of speed to abrade or cut away at the obstruction. The burr is a solid tip that is introduced into the vessel with a catheter and remotely driven to rotate at the desired speed. The burr is introduced into the patient's body typically at the femoral artery and guided to the obstructed vessel.
The rotatable burr atherectomy devices of the prior art when properly used have several advantages over the balloon angioplasty technique. Unlike the balloon angioplasty technique, treating an occluded vessel with a rotatable burr essentially completely removes the obstructing material, leaving the vessel wall relatively smooth and eliminating the bits or flaps of tissue at the treatment site which often result from balloon angioplasty. Moreover, unlike the balloon angioplasty device, a rotatable burr can effectively remove eccentric occlusions, because the rotating burr tends to "slide off" the healthy vascular tissue on one side of the vessel and to selectively abrade the occluding material on the other side of the vessel. Furthermore, a rotatable burr, which abrades as it progresses, can effectively treat a relatively long occlusion, and tight and/or calcified occlusions.
One major drawback with traditional rotatable burr atherectomy devices is that they have a fixed working diameter. That is, the cutting size is fixed and cannot be varied to accommodate a range of vessel openings. When it is necessary to clear a relatively large vessel which has become severely occluded, typically a physician will be reluctant to use a burr of sufficient diameter to clear the vessel all at once. This necessitates the use of two or more successively larger diameter burrs. Moreover, many times the prior art atherectomy procedure must be assisted by a balloon procedure in order to achieve an adequate result. The above tends to lengthen and complicate the procedure and make it costly. In order to get a large diameter burr to the site of the obstruction, it must first be introduced into the patient's body through an introducer sheath, typically in the patient's leg, and guided through the patient's vascular system to the obstructed vessel. Large burrs require appropriately large introducer sheaths, which tend to cause increased vascular tissue trauma at the site of introduction. Large burrs also tend to cause increased vascular tissue trauma as they are guided through the patient's vascular system to the obstruction site. Large burrs might also interfere with or disturb other occlusions along the way to the target occlusion, such other occlusions being otherwise too small to indicate treatment. For example, it has been found that it is better not to treat or disturb occlusions of less than about 50%-60%, since treatment of such lesions entails greater risks to the patient's health than leaving them untreated or undisturbed. A large diameter burr could tend to disturb such small lesions in passage, even to the extent that they become health-threatening. In addition, because prior art burrs have had an abrading surface on only their forward or distal surfaces, physicians have encountered difficulty in satisfactorily treating occlusions at curved vessel locations. Accordingly, physicians faced with the prospects of having to introduce, guide, and then manipulate in the obstructed area a relatively large burr might choose to avoid the rotatable burr technique altogether and fall back to a less desirable alternative, such as balloon angioplasty or even bypass surgery.
Thus, there is a clear need in the medical community for an atherectomy device which possesses all the advantages of the traditional rotatable burr device over the balloon angioplasty technique, but yet can be introduced into the patient's body with a relatively small introducer sheath, thus minimizing tissue trauma at the introduction site; can be guided to the obstruction site with minimal vascular tissue trauma and using smaller guiding catheters; can pass through non-targeted (smaller) occlusions with minimal contact; and can be used to treat openings of varying size during the same procedure. It will be appreciated that such a device would eliminate the need for multiple procedures with varying sized burrs, and would eliminate the reluctance of physicians to use the rotatable burr technique in the first place due to the disadvantages they see with the larger, fixed diameter burrs. There is also a need for such a device having an abrading surface on its proximal face as well as on its distal face, to facilitate treating occlusions at curved vessel sites.
Other atherectomy devices with rotatable expandable blades have been disclosed in U.S. Pat. No. 4,966,604 to Reiss and U.S. Pat. No. 4,895,560 to Papantonakos. Although the blades expand to accommodate variable vessel size, sensor devices or other means must be used during the expansion of the instrument and cutting because the blades can injure or puncture the vessel to be repaired in addition to cutting away the obstruction.